1. Field of the Invention
This invention relates to an improvement in a motor drive device for a camera using a motor for at least one operation such as film winding, film rewinding and charging of a charge mechanism.
2. Description of the Prior Art
In the conventional motor drive device for a camera, the reduction ratio thereof has been set at a value which does not permit the use of a motor either at the maximum output point or at the maximum efficiency point thereof, because: With the reduction ratio set at a value enabling use of the motor at the maximum output point thereof, the length of time required for charging the camera can be shortened for normal photography. However, in this case, on the other hand, the number of rolls of film which can be fed decreases since the battery of the camera is discharged faster. Furthermore, under a low temperature condition, such as -20.degree. C. or the like, the film load increases by 3 to 4 times as much as the load under normal temperatures and, when a manganese battery is used as the power source, the internal resistance thereof greatly increases to hinder the flow of current. Then, under such a condition, the output torque of the motor decreases making it difficult to start the motor. When the reduction ratio is set to permit use of the motor at the maximum efficiency point, a greater number of film rolls can be fed and the camera can be charged even in low temperatures. However, under normal temperatures film winding requires a longer period of time. This is a serious problem for a motor drive device which is required to wind up 5 to 6 photography frames of film per second. To avoid these problems, therefore, motor drive devices in general have the reduction ratio set at a value corresponding to a middle point between the maximum output point and the maximum efficiency point of the motor. However, the conventional arrangement, so to speak, impairs the above two advantages.